1. Field of the Invention
The present invention relates to a superconductive cable containing several wire strands sheathed by a highly resistive, non-magnetic, thermally conductive material. Each wire strand consists of a plurality of twisted wires with each wire containing a plurality of filaments of a superconductive material embedded in a matrix material.
2. Description of the Prior Art
The structure of a superconductive cable made of wires containing very thin filaments of a superconductive material embedded in a matrix material is advantageous because wires of this kind have relatively minor magnetic instabilities and low magnetic losses in the filaments. However, this advantage is countered by a disadvantage in that the magnetic fields created by the filaments whenever the current is switched on and by any other time-variable, changing magnetic fields, act to induce eddy currents in the normally conductive matrix material even at extremely low temperatures. These induced currents partially flow within the superconductive filaments and, for this reason, are very slow to disappear.
In order to prevent, as far as possible, induced currents within the matrix material, two measures have been used up to now. The wire is twisted around its longitudinal axis and several wires are either formed into a strand or interlaced to form a ribbon. In addition, each wire and each stranded wire are sheathed by a material having a high resistance. This high resistance material must not be magnetic and should have good thermal conductivity such that the magnetic field created by the current in the superconductive filaments is not impeded and the heat created in the wires may be carried away easily.
The described disadvantage is magnified further whenever the superconductive cable is used in the construction of a very powerful electro-magnet, which will come under the influence of another highly powerful periodically varying magnetic field, as, for instance, in certain plants destined for use with nuclear fusion.